The present invention relates to a novel multi-functional additive composition which improves the cold operability of middle distillates, in particular in the course of the processes of slow cooling during the storage of fuels and combustibles at low temperatures. The invention is directed in particular toward improving the antisedimentation properties for an application in fuels for diesel engines and in combustibles such as domestic fuel oils for boilers.
Cold operability corresponds to a limit temperature at which the middle distillates may be used without any problems of clogging. It is intermediate between the cloud point (ASTM D 2500-66), characteristic of the start of crystallization of paraffins in the distillate, and the pour point of this distillate (ASTM D 97-66).
It is well known that the crystallization of paraffins is a limiting factor in the use of middle distillates. Thus, it is important to prepare diesel fuels that are suitable for the temperatures at which they will be used in motor vehicles, that is to say for the surrounding climate. Generally, a cold operability for fuels of xe2x88x9210xc2x0 C. is sufficient in many industrialized countries. However, in other countries such as the Scandinavian countries, Canada and the countries of north Asia, fuel working temperatures of well below xe2x88x9220xc2x0 C. can be expected. This is likewise the case for domestic fuel oils stored outside for private houses and buildings.
This suitability of the cold operability of diesel fuels is important, especially when the engines are being started cold. If paraffins are crystallized at the bottom of the tank, they can be drawn into the engine on starting and can block in particular the filters and prefilters arranged before the injection systems (pump and injectors). Similarly, in the case of the storage of domestic fuel oils, paraffins precipitate at the bottom of the tank and can be drawn in and obstruct the pipes before the pump and the boiler feed system (injection nozzle and filter). Obviously, the presence of solids, such as paraffin crystals, prevents the normal circulation of the middle distillate.
To improve their circulation either in an engine or toward boilers, several types of additives have come to light.
In a first stage, the oil industry concentrated on the development of additives which promote the filterability of fuels at low temperature. The role of these additives, known as cold filter-plugging point (CFPP) additives, is to limit the size of the paraffin crystals formed. Additives of this type, which are widely known to those skilled in the art, are currently systematically added to middle distillates.
However, these additives, although controlling the size of the paraffin crystals, cannot prevent the sedimentation of the crystals formed, that is to say their agglomeration, especially at the bottom of the fuel tanks of diesel vehicles when stationary or in storage tanks for domestic fuel oils.
Thus, in a second stage, the oil industry made efforts to develop antisedimentation additives, that is to say dispersants, which keep the paraffin crystals in suspension in the middle distillate, thus preventing them from depositing and agglomerating together. The Applicant has especially developed such an additive described in patent EP 0 674 689.
Nevertheless, the joint action of CFPP and anti-sedimentation additives has not made it possible to improve the cold operability of all the middle distillates produced in refining in the case of all the known crude oils.
This is why the oil industry has introduced a third type of additive with a view to lowering the cold operability temperature of middle distillates, whatever they be, beyond xe2x88x9220xc2x0 C., even if their cloud point is above xe2x88x9220xc2x0 C. This is the case for the additives described in patents EP 0 722 481 and EP 0 832 172. However, this set of additives shows good operability properties depending on the cold regimes when compared with measures which have been taken by cold immersion, according to NF standard M 07 085, of fuels and combustibles containing such additives. However, although this method makes it possible to judge the efficacy of the additives, it is not rigorously representative of the actual cooling phenomena of fuels and combustibles. Thus, the amplitude and speed of cooling are variable depending on the region, and thus depending on the ambient temperature of the vehicles. A slow cooling is very favorable toward gradual sedimentation of paraffins, and thus it is necessary to find solutions to prevent this phenomenon.
The present invention is directed toward a multifunctional additive composition for lowering and maintaining the cold operability temperature of middle distillates, so that during a step of slow cooling on storage in a closed container, down to temperatures beyond xe2x88x9220xc2x0 C., no sedimentation of the paraffins contained in the middle distillates is observed.
One subject of the present increase is thus a multifunctional additive composition for the cold operability of middle distillates resulting from the reaction of carboxylic compounds with amine compounds, characterized in that it contains at least 50% by weight of a mixture consisting of:
a) 10% to 90% by weight of an additive (AB) resulting from the reaction of at least one carboxylic compound (A) chosen from alkylmaleic and alkenylmaleic anhydrides and alkylsuccinic and alkenylsuccinic anhydrides containing from 4 to 32 carbon atoms in the alkyl and alkenyl radicals, the corresponding acids and esters with at least one polyalkyleneamine (B) of general formula (I) below:
NH2xe2x80x94[(CH2)nxe2x80x94NHxe2x80x94]mxe2x80x94Hxe2x80x83xe2x80x83(I)
xe2x80x83in which n is an integer ranging from 2 to 4 and m is an integer ranging from 1 to 4, the molar ratio A/B being between   1      m    +    1  
xe2x80x83and m+1, and preferably between 1 and 2,
b) and 90% to 10% by weight of an additive (CD) resulting from the reaction:
i) of at least one copolymer (C) resulting from the reaction of at least one first unsaturated carboxylic acid which may be unsubstituted or substituted with at least one alkyl ester of at least one second substituted or unsubstituted unsaturated carboxylic acid, which may be identical to or different from the first, of general formula (II) below: 
xe2x80x83in which R1 and R2, which may be identical or different, are chosen from the group consisting of hydrogen and linear or branched alkyl groups containing from 1 to 20 carbon atoms, R3 is hydrogen or a linear alkyl group of not more than 3 carbon atoms and R4 is hydrogen or an alkyl group containing from 1 to 25 carbon atoms,
ii) with an N-alkylpolyalkylenepolyamine (D) of general formula (III) below:
R5xe2x80x94NHxe2x80x94[xe2x80x94(CH2)pxe2x80x94NHxe2x80x94]qxe2x80x94Hxe2x80x83xe2x80x83(III)
xe2x80x83in which R5 is a saturated aliphatic radical comprising from 1 to 32 carbon atoms, p is an integer ranging between 2 and 4 and q is an integer ranging between 1 and 4, the molar ratio C/D ranging between   1      q    +    1  
xe2x80x83and q+1, and preferably ranging between 1 and 2.
The combination of these two reaction products (AB) and (CD) in the composition according to the invention has made it possible to very significantly improve the cold operability of fuels and combustibles into which they are incorporated for a slow cooling, when compared with the efficacy of these products taken separately.
To compare the efficacy of this additive composition with the additives known in the prior art, the Applicant developed a new test based on NFT standard M 07 085 in which the procedure of rapid cooling by immersion has been replaced with a slow and controlled cooling of the temperature, for example by 1 to 3 degrees per minute, down to a nominal temperature, for example xe2x88x9220xc2x0 C.
More specifically, the additive according to the invention consists of:
50% to 100% by weight of the combination containing from 20% to 80% by weight of the additive AB and from 80% to 20% by weight of the additive CD, and
0% to 50% by weight of a combination of the additives AD and CB obtained by reacting A and D in a molar ratio ranging between 0.2 and 4, and of B with C in a molar ratio ranging between 0.2 and 4, A, B, C and D having been defined beforehand for the multifunctional additives AB and CD.
In a first embodiment, the additive composition is obtained by combination of 50% to 80% of AB and 20% to 50% by weight of the reaction product CD.
In a second embodiment, the additive composition comprises from 50% to 80% by weight of a combination AB,CD in an AB/CD molar ratio ranging from 0.2 to 4, and from 20% to 50% by weight of a mixture of AD,CB in 20 an AD/CB molar ratio ranging from 0.2 to 4.
The carboxylic compound (A) is preferably chosen from the group comprising dodecylmaleic anhydride, dodecenylmaleic anhydride, hexadecylmaleic anhydride, hexadecenylmaleic anhydride, octadecylmaleic anhydride, octadecenylmaleic anhydride, eicosylmaleic anhydride and eicosenylmaleic anhydride.
The polyalkyleneamine (B) is preferably chosen from the group comprising diethylenetriamine, dipropylenetriamine, triethylenetetramine, tripropylenetetramine, tetraethylenepentamine and tetrapropylenepentamine.
The copolymer (C) is preferably a copolymer containing from 45 mol % to 65 mol % of at least one carboxylic acid unit and from 55 mol % to 35 mol % of at least one alkyl ester unit. The carboxylic acid units are preferably chosen from units resulting from acrylic acid and methacrylic acid, and the alkyl ester units are preferably chosen from units resulting from acrylic esters and methacrylic esters, and derivatives thereof. In a more favorable mode, the copolymer (C) is chosen from acrylic acid/methacrylic ester copolymers and methacrylic acid/acrylic ester copolymers containing 45 mol % to 65 mol % of acid units and from 55 mol % to 35 mol % of ester units.
The N-alkylpolyalkylenepolyamine (D) is preferably chosen from the group comprising N-alkylethylenediamines, N-alkylpropylenediamines, N-alkylbutylenediamines, N-alkyldiethylenetriamines, N-alkyldi-propylenetriamines, N-alkyldibutylenetriamines, N-alkyltriethylenetetramines, N-alkyltripropylene-tetramines and N-alkyltributylenetetramines with an alkyl radical containing from 12 to 22 carbon atoms. Preferably, D is chosen from N-dodecyldipropylenetriamine, N-octadecyldipropylenetriamine, N-octadecyldiethylenetriamine and N-docosyldiethylenetriamine.
A second subject of the invention is a fuel containing a majority of middle distillate generally containing a filterability additive, and a minority, for example from 50 to 1000 ppm, of a multifunctional additive composition for cold operability for slow cooling.
It would not constitute a departure from the context of the invention if proketane additives, detergents, additives with a pour point and a cloud point, antifoam additives, demulcents, anticorrosion additives and antioxidants were added to this fuel.